In some conventional audio and vide units for example, audio or video signal is transmitted by digital signal to effectively avoid deterioration of sound or image quality.
An audio unit will be described by way of example. When an audio signal played back by a compact disc player for example is recorded by a mini disc player, the compact disc player modulates a played-back digital audio signal based on a clock of the digital audio signal before outputting the audio signal to the mini disc player. On the other hand, the mini disc player to receive the digital audio signal from the compact disc player uses a PLL circuit to extract the clock from the digital signal transmitted from the compact disc player, and then plays back the received digital audio signal based on the extracted clock. Thereby, the mini disc player processes, or records for example, the received digital audio signal synchronously with the clock of the digital audio signal transmitted from the compact disc player.
That is, for transmission of a digital audio signal or digital video signal, the receiving side will operate synchronously with the clock of the received digital audio or video signal.
Signal transmission with a plurality of units connected to the bus line defined by the IEEE 1394 for example will be discussed herebelow. In this case, a digital audio or video signal played back from a disc or the like in one playback unit or player is sent to the bus line and received and recorded by a recording unit or recorder also connected to the bus line.
To record the digital audio or video signal, it is necessary that the player should be completely synchronous with the recorder. Desirably, no jitter should be contained in the transmitted digital signal. However, it is difficult to completely eliminate the jitter.
For synchronization between the playback operation of the player and recording operation of the recorder, it is possible that control data on the playback operation, etc. is transmitted via a bus line for synchronization between the two units, namely, between the player and recorder. However, since more than two units can be connected to the bus line defined in the IEEE 1394 for example and data can be transmitted at a plurality of rates over the bus line, so if in the middle of a digital signal output of a player being recorded in a recorder, the player has received a different rate control command from any other unit, the recorder will not be able to record the digital signal normally, namely, fail in recording the digital signal.